Contaminant-activated photocatalysis

ABSTRACT

A visible light photocatalyst coating includes a metal oxide that in the presence of a organic contaminate that absorbs at least some visible light or includes the metal oxide and an auxiliary visible light absorbent, where upon absorption of degradation of the organic contaminate occurs. Contaminates can be microbes, such as bacteria, viruses, or fungi. The metal oxide is nanoparticulate or microparticulate. The metal oxide can be TiO 2 . The coating can include an auxiliary dye having an absorbance of light in at least a portion of the visible spectrum. The coating can include a suspending agent, such as NaOH. The visible light photocatalyst coating can cover a surface of a device that is commonly handled or touched, such as a door knob, rail, or counter.

CROSS-REFERENCE TO A RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser.No. 62/368,357, filed Jul. 29, 2016, the disclosure of which is herebyincorporated by reference in its entirety, including all figures, tablesand drawings.

This invention was made with government support under Grant No. 1127830awarded by the National Science Foundation and Grant No. 0749481 awardedby the National Science Foundation. The government has certain rights inthe invention.

BACKGROUND OF INVENTION

Patients and visitors in healthcare facilities can acquire infections bydirect or indirect contact with common surfaces (room door handles, bedrails, taps, sterile packaging, mops, ward fabrics and plastics,keyboards and telephones) that have become contaminated with pathogenicmicrobes. Making these surfaces microbe-unfriendly can break the cycleof contamination and infection. Antiadhesive coating, e.g., Sharklet,Pilkington, are limited in that they do not kill microbes. Polycationiccoatings, e.g., microban, have short lifetime, expensive and microbesgain resistance over time. Antimicrobial coatings that releasemicrobiocides, e.g., AgION, SilvaGard, are expensive and microbes gainresistance with time. Others that release toxic silver or copper ions,which are currently in clinical trials, have limited lifetimes, aredifficult to apply, and are costly. Further, copper surfaces wereunsuccessful in reducing bacterial concentrations to the benign level inclinical trials.

TiO₂ photocatalysis has attracted intense interest for applications inself-cleaning and antimicrobial coatings as TiO₂ can completelymineralize organic contaminants including microorganisms and the processproduces no toxic by-products. Further, TiO₂ is environmentally benignand inexpensive. Unfortunately, TiO₂, which is an excellentphotocatalyst under UV light, has very limited capability for visiblelight absorption, which limits its utility in an normal interior surfaceof a building. Strategies at modifying the crystal structure of TiO₂ toextend its absorption band into the visible region have not led to aproven and widely adopted photocatalytic system.

A manner that allows TiO₂ or other transition metal oxides, alkali metaloxides, or alkali earth metal oxides to degrade organic contaminantsincluding bacteria under visible light is desirable. Furthermore,achievement of transparent, visible light activated photocatalyticcoatings to prevent healthcare-acquired infections is desirable.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a stylized hypothetical mechanism of contaminant-activatedvisible light photocatalysis coatings, according to an embodiment of theinvention.

FIG. 1B shows a plot of the pseudo first order degradation rate vswavelength superimposed on the absorbance spectrum of Mordant Orange(MO) using various long pass optical filters where the percentage is therelative contribution to the overall degradation rate of 0.01 hr⁻¹ withN=4.

FIG. 1C shows a plot of the pseudo first order degradation rate vswavelength superimposed on the absorbance spectrum of Procion Red (PR)using various long pass optical filters where the percentage is therelative contribution to the overall degradation rate of 0.023 hr ⁻¹with N=4.

FIG. 2A is a bar chart of Pseudo first order rate coefficients fordegradation of MO on anatase coatings, according to embodiments of theinvention, using full or partial visible spectra where dark controlmeasures the ability of anatase coating to degrade MO in dark and lightcontrol measures the ability of MO degradation by light on anonphotocatalytic surface (silica) where N=4.

FIG. 2B is a bar chart of Pseudo first order rate coefficients fordegradation of PR on anatase coatings, according to embodiments of theinvention, using full or partial visible spectra where dark controlmeasures the ability of anatase coating to degrade PR in dark and lightcontrol measures the ability of PR degradation by light on anonphotocatalytic surface (silica) where N=4.

FIG. 3 represents the relative rates for different visible lightintensity on pseudo first order rate coefficients for MO degradation onanatase coating, according to an embodiment of the invention, withsingularly and multiply covered samples where no statisticallysignificant decrease in rate coefficient is observed with the 26%decrease in visible light intensity where N=4.

FIG. 4A is a stylized hypothetical mechanism of contaminant-activatedvisible light photocatalysis with auxiliary light harvester polyhydroxyfullerene (PHF) coatings, according to an embodiment of the invention.

FIG. 4B shows a bar chart of pseudo first order rate coefficients fordegradation of MO on anatase and anatase+PHF coatings, according toembodiments of the invention, where the dark control measures theability of the photocatalytic coatings to degrade dye in the dark withN=10.

FIG. 5 is a visible light absorption spectrum for polyhydroxyfullerenes.

FIG. 6 represents the relative rates for titanium dioxide crystalpolymorph photocatalyst, according to embodiments of the invention,where the on pseudo first order degradation rate coefficients for MOdegradation using rutile/anatase and anatase/anatase and coatings, whereno statistically significant increase in rate coefficient is observedwith replacement of anatase with rutile with N=10.

FIG. 7 is a composite plot of band gap energies for anatase (3.2 eV) andrutile (3.03 eV) powders estimated from UV-Vis absorption spectra.

FIG. 8 is comparative TIO₂ photocatalyst coatings, according to anembodiment of the invention, at different particle loading of a) 0mg/cm²; b) 0.128 mg/cm²; c) 1.28 mg/cm²; and d) 6.4 mg/cm².

FIG. 9 indicates the effect of different dispersants on effectiveparticle size and zeta potential for TiO² photocatalyst formulationcoatings, according to embodiments of the invention, and the performanceof the contaminant-activated photocatalysis with PR.

FIG. 10 shows the effective stability of various TiO₂ suspensions atdifferent pH over time for the preparation of the TIO₂ photocatalystcoatings, according to an embodiment of the invention.

FIG. 11A is a scanning electron micrograph of rutile/anatase coatingsprepared from a formulation without any dispersant, according to anembodiment of the invention.

FIG. 11B is a scanning electron micrograph of rutile/anatase coatingsprepared from formulation with 0.01 M NaOH as a dispersant, according toan embodiment of the invention.

FIG. 12 is a bar chart of pseudo first order rate coefficients forinactivation of Staphylococcus aureus on various coatings, according toembodiments of the invention, where the dark control measures theability of the rutile/anatase+0.1PHF coatings to inactivate bacteria inthe dark and the rutile control measures the ability of rutile/silicacoatings to inactivate bacteria in light with N=6.

FIG. 13 is a visible light absorption spectrum for Staphylococcus aureuson anatase coatings, according to an embodiment of the invention.

FIG. 14 is a bar chart for the reduction in bacterial burden on varioussurfaces coated with photocatalyst coatings, according to embodiments ofthe invention, where bars represent counts at times from 0 to 12 monthswhere the surfaces are: W=Wall; T=Thermostat;

L=Locker; K=Knob; D=Soap Dispenser; R=Bathroom Rail; B=Bed Rail; andC=Counter with (N=3 and where lower dashed line indicate the thresholdof microbial counts for benign surfaces and the upper dashed lineindicates the average microbial counts on a copper surface.

DETAILED DISCLOSURE

Embodiments of the invention are directed to photocatalysts that resultfrom contaminate activation by TiO₂ or other metal oxide, such as theoxides of vanadium, chromium, titanium, zinc, tin, and cerium, ore eventhose of alkali metal oxides or alkali earth metal oxides. FIG. 1Aillustrates the hypothetical mechanism of contaminant activated visiblelight photocatalysis. Visible light is absorbed by the contaminant,generating electron-hole pairs (excitons). Electrons are scavenged fromthe contaminant by anatase, a naturally occurring polymorph of TiO₂ withhigh electron affinity. These electrons react with oxygen and water atthe surface of anatase particles forming highly labile oxygen species,such as superoxide radicals and hydroxyl radicals (ROS) that, in turn,decompose the contaminant. It has been discovered that although theparticles can be microparticles or nanoparticles, the particles mustcontain sub-50 nm crystallites, for example, less than 40 nm, less than30 nm, less than 20 nm, and less than 10 nm. Anatase with 22, 10 and 7nm crystallites form very effective contaminate activated visible lightphotocatalytic systems.

The contaminant degradation is dependent on overlap between thecontaminant's absorption spectrum and the incident light spectrum.Contaminate can be microbes or organic compounds with a chromophore thathas some absorbance of visible light. Optical long-pass filters wereused to effectively create several wavelength bands in the regionbetween 385 nm, which is the lower limit of emission of the fluorescentlamps employed experimentally, and 800 nm, the nominal upper limit ofvisible light. According Mordant Orange (MO), which absorbs moststrongly at 400 nm, degrades fastest with light in this wavelengthregion. This was confirmed experimentally, as shown in FIG. 1B.Similarly, Procion Red (PR), with an absorption peak at 520 nm, wasdegraded most rapidly within the wavelength band of 495 to 550 nm asshown in FIG. 1C. Controls consisting of dye on a non-photocatalyticsurface (silica) and dye on anatase in darkness showed effectively noactivity FIGS. 2A and 2B, indicating that both anatase and visible lightare required for degradation. The optical filters introduced a slightdecrease in overall light intensity with increasing cutoff wavelength,but the modest decrease of this same order was shown to have negligibleeffect on the photocatalytic degradation rate (FIG. 2). Therefore, undervisible light the rate of photocatalysis correlates strongly with thelight absorption by organic contaminants.

An auxiliary visible light absorbent, such as a dye, enhancesphotocatalytic degradation through increased exciton generation and,concomitantly, electron transport to anatase where ROS's are formed FIG.4A. Polyhydroxy fullerenes (PHF), has broadband absorption, as shown inFIG. 5 and has a high degree of stability, and is therefore well suitedas an auxiliary visible light absorbent. Other carbon species, such asfullerenes, carbon onions, or graphene can function as the auxiliaryvisible light absorbent. As shown in FIG. 4B, incorporation of PHF inthe anatase coating increases the degradation rate by up to 2.5 times,depending on wavelength. The largest effect was observed with lightbetween 400 nm and 495 nm. Minimal wavelength cutoffs grater than 490 nmled to very low rates with or without PHF.

Rutile can act as an enhancer for visible light activity of anatase. Themixed phase coating prepared by depositing a rutile coating followed bydeposition of an anatase coating when compared with two layer coatingsof anatase shows a slight improvement in photocatalytic rate at lightbetween 400 nm and 495 nm, as indicated in FIG. 6. This is consistentwith the absorption edge for rutile, which slightly extends into thevisible region to 410 nm as shown in FIG. 7.

Transparent photocatalytic coatings are obtained when the particleloading is equal to128 μg/cm², which yields a nominal thickness of 0.25μm, as shown in FIG. 8. In an embodiment of the invention, the metaloxide, TiO₂, is deposited from a suspension of the metal oxide. Thesuspension can be in water, ethanol, toluene, or other liquid medium.Settling of TiO₂ particles from a depositing suspension over time canlead to non-uniform coating. Formulation can be stabilized by additivesthat promote electrostatic (NaOH), steric (Tween 20), or a combinedelectrostatic and steric (sodium dodecyl sulfate) interactions.Electrostatic stabilization stabilizes a formulation without impairingthe coating's photocatalytic activity, as shown in FIG. 9. A NaOHcomprising coating formulation with pH between 9 and 10 was stable forone week, as illustrated in FIG. 10. The effect of dispersant on thecoating uniformity is apparent from scanning electron microscopy, asshown in FIG. 11. In the absence of dispersant, the coating consisted of10-100 μm agglomerates, whereas in coating prepared with 0.01 M NaOH,the coating consisted primarily of agglomerates of less than 1 μm insize.

Bactericidal activity of fully optimized photocatalytic coatings wascompared to coatings lacking PHF and coatings lacking anatase and PHF. Abenign strain of the pale yellow-colored bacterium, Staphylococcusaureus (ATCC 25923), was used as a model for MRSA, which is often thecause of healthcare-acquired infections. Photocatalysis inactivatescells by degrading the cell surface. Because most MRSA strains do notexpress a capsule, the efficacy of photocatalysis against MRSA should beequal to or superior to that of S. aureus examined.

The fully optimized coating that consisting of anatase, rutile, and ahigh concentration of PHF displays a rapid rate of bacterialdegradation, as indicated in FIG. 12. Coatings that consisted of anataseand rutile, which absorbs visible light only up to a wavelength of 409nm, gave a bacterial degradation rate 64% of the rate observed with PHF.Addition of rutile to anatase coatings, as indicated above, gave onlymarginally better Mordant Orange degradation than anatase alone. S.aureus exhibits peak absorption at 430 nm with a bandwidth of 150 nm, asshown in FIG. 13. Omission of anatase from the coating decreased itsbactericidal activity by only 30%. Thus, photocatalytic degradation ofbacterial cell mass is activated by light absorption and concomitantexciton generation within the bacterial cells.

The antimicrobial coating was further evaluated for its ability tocontrol the microbial burden on surfaces in a beta facility. Patients inhealthcare facilities can acquire infections by direct or indirectcontact with common surfaces, for example, room door handles, bed rails,taps, sterile packaging, mops, ward fabrics and plastics, keyboards andtelephones that have become contaminated with pathogenic microbes.Making these surfaces microbe-unfriendly can break the cycle ofcontamination and infection. Antimicrobial coatings that slowly releasetoxic silver or copper ions, currently in clinical trials have limitedlifetime, are difficult to apply and are costly. The best performingprior art antimicrobial coating in clinical trials, copper, wasunsuccessful in reducing bacterial concentrations to a benign level.

Surfaces that were initially steamed and allowed to dry for 15 minuteswere coated with BioShield NuTiO primer, and allowed to dry for another15 minutes. The primer was provided as a binding agent for theantimicrobial coating. The antimicrobial coating was applied to theprimer coating using a commercial fogger. Selected surfaces were sampledwithin 1 hour of coating, and again at 2, 4, 6 and 12 months, as shownin FIG. 14. As shown in FIG. 14, surfaces are arranged along the x-axisfrom left to right in order of presumed increased frequency of contact.The temporal variation of bacterial counts on each surface is indicatedby a sequence of five bars. The wall (W) and thermostat (T) had initialbacterial counts below the benign limit of 2.5 CFU/cm² (6 CFU/4 sq.in.)proposed by Griffith et al

No significant change in bacterial count was observed on the wall,whereas the count on the thermostat decreased by 93% after 12 months.Initial bacterial counts on both lockers (L) and door knobs (K) greatlyexceeded the benign limit. Counts decreased by 99% within 2 months andremained within the benign range for the duration of the study. Soapdispensers (D) had low counts (below benign limit), possibly due toantimicrobial agents used in the soap. Initial bacterial counts onbathroom rails (R) and bed rails (B) were above the benign limit, withbed rails exhibiting the highest initial counts among all surfacesstudied. Bacterial counts on these two surfaces decreased significantlythroughout the study.

Bacterial levels on the kitchen counter (C) were very high initially andremained above the benign limit for all but the last sampling. Of thefive surfaces with initial bacterial counts above the benign level, onlythe kitchen counter failed to exhibit consistently good performance.This is possibly due to frequent wiping (several times daily), which mayhave removed the antimicrobial coating. The incidence of acquiredinfections in the beta facility during the first six months of the studywas reduced by 55% compared to the previous year. The beta facilityresults suggest that contaminant-activated photocatalysis can transformcommon indoor surfaces into antimicrobial surfaces with potential tobreak the cycle of contamination and infection.

Visible light absorbing organic contaminants, including bacteriaactivate pristine titanium dioxide, are visible light photocatalysis fortheir self-degradation. Hence, highly efficacious and cost-effectiveantimicrobial coating that is easy to apply and lasts for at least oneyear are available. The contaminant-activated photocatalysis has broadimplications in design of paints, pharmaceuticals, food additives,polymer composites, cosmetics, catalysts and antimicrobial coatings.

Methods and Materials

Photocatalytic coating formulation was prepared by adding 10 mg ofanatase (A7) to 10 mL of dilute NaOH (pH=9.5) in a 20 mL scintillationvial wrapped with aluminum foil. The suspension was sonicated (MisonixSonicator 3000, Farmingdale, NY) at the highest power level providing180-200 W for 30 minutes total (10 min on/2 min off×3). Similarly,rutile (R22) and silica (S15) coating formulations were prepared withoutexposing to visible light. In case of anatase+PHF, the anatasesuspension was sonicated for 30 minutes followed by addition of 1 mL ofa PHF solution (1000 or 100 mg/L). The nanocomposites suspension wasmixed with a magnetic stirrer for 10 minutes in dark.

Ceramic tiles were utilized to evaluate the photocatalytic degradationof organic dye and inactivation of microbes. A volume of 0.4 mL of aselected coating formulation was pipetted on the tile surface as thefirst coat. The coated surfaces were dried for one hour at 40° C. indark. A second coat of the same or a different coating formulation wasapplied following the same procedure. A total surface loading of 128μg/cm was achieved using this procedure. Organic dye or S. aureussuspension was applied to the test surfaces. In case of an organic dye,0.02 mL of PR solution (2000 mg/L) or MO solution (2000 mg/L) waspipetted onto coated tiles and allowed to spread. The dye-coated tileswere dried at 50° C. for 20 minutes in dark before starting theperformance evaluation. In case of S. aureus, 0.1 mL of S. aureussuspension (2-3×10⁵ CFU/mL) was pipetted onto each coated tile surfaceand allowed to spread, giving a surface loading of 6400-9600 CFU/cm2.The tiles with S. aureus were dried in the dark in a biosafety cabinetfor 3 hours.

A Perkin-Elmer Lambda 800 UV/VIS spectrophotometer with PELA-1000reflectance accessory was used to measure light adsorption by TiO₂ overa range of 300 to 700 nm. The band gap energy was determined fromE=hc/λ, where λ us the wavelength at which a strong cutoff in absorptionis observed, h is the Plank constant (4.14×10-15 eV.$) and c is thespeed of light in vacuum (3.00×108 m/s). A white Teflon plate was usedas the internal reference. The band gaps for anatase and rutile weredetermined from UV3 Visible absorption measurements to be 3.2 eV for A7and 3.03 eV for R22. The crystal type and the size of crystallite wasdetermined with X-ray diffraction on an APD 3720 diffractometer(Philips, Andover, Mass.) with Cu-Kα radiation (40 kV, 25 mA) anddiffracted beam monochromator, using a step scan mode with the step of0.075° (20) and 4 s per step. Crystal structure was identified accordingto the database of International Centre for Diffraction Data (ICDD). Thecrystallite size was determined from the Scherrer equation:

$L = \frac{K\lambda}{\left( {B - b} \right)\cos \theta}$

where L is the average crystallite size, K is the shape factor (0.9), Ais the X-ray wavelength of Cu-Kα radiation (1.54 A), B is the overallline broadening in radians at the full width at half maximum (FWHM)intensity, b is the line broadening in radians at the FWHM intensitycaused by the instrument itself (0.07) and 0 is the Bragg angle, i.e.,the angle at which highest intensity was observed. X-ray diffractionpatterns of anatase and rutile are in good agreement with the anataseand rutile crystalline structures given in the ICDD database.Photocatalysts utilized in the antimicrobial coatings were anatase andrutile with 7 nm and 22 nm primary crystallite sizes, respectively.

The purity of TiO₂ powders (anatase and rutile) was determined withX-ray photoelectron spectroscopy (XPS) (Perkin-Elmer PHI 5100ESCAsystem). The data obtained was analyzed with AugerScan software (ThermoFisher Scientific, Waltham, Mass.). X-ray photoelectron spectraindicated the presence of titanium, oxygen and adventitious carbon ineach powder. Rutile also included a small amount (4.9 atomic %) ofaluminum, potentially from the aluminum substrate. Both powders werepure white in color.

Specific surface area of anatase and rutile was measured under nitrogenusing a NOVA 1200 with multipoint BET (Quantachrome Instruments, BoyntonBeach, Fla.). TiO₂ powder was degassed and dried under vacuum at 110° C.prior to measurement.

Scanning electron microscopy (JOEL 6335F FEG-SEM) was used to observethe ultrastructure of TiO₂ coating at the conditions of 10 kVaccelerating voltage and 10 mm working distance.

Staphylococcus aureus (ATCC 25923) was obtained from American TypeCulture Collection (Manassas, Va.). Tryptic soy agar and tryptic soybroth (Becton, Dickinson and Company, Sparks, Md.) were used forculturing and enumerating the bacteria. A mass of 40 g Tryptic soy agarpowder was suspended in 1 L of deionized water and mixed thoroughly withheating to the boiling point. The solution was autoclaved at 120° C. and16 bar for 15 minutes. Plates were made by pouring the autoclaved agarinto 100×15 mm sterile plastic Petri dishes (Fisher Scientific) and airdried in a laminar flow hood (LABCONCO purifier class 2 safe cabinet)for 24 hours. The dried agar plates were used immediately or stored ininverted position in a refrigerator at 4° C. Broth was prepared byadding a mass of 32 g tryptic soy broth powder to 1 L of deionized waterand mixing thoroughly with heating to the boiling point. The broth wasautoclaved at 120° C. and 16 bar for 20 minutes. Autoclaved broth wasused immediately or stored in a refrigerator at 4° C. Phosphate-bufferedsaline (PBS) solution was prepared by dissolving 12.36 g Na₂HPO₄, 1.8 gNaH₂PO₄ and 85 g NaCl in 1000 mL of deionized water and then diluting10× immediately before use. PBS/SDS solution was prepared by adding0.576 g sodium dodecyl sulfate (SDS) to 1000 mL of PBS and thenautoclaving at 120° C. and 16 bar for 15 minutes.

The S. aureus culture was maintained by streaking the bacteria ontryptic soy agar in a Petri dish. The inoculated plate was inverted andincubated at 37° C. for 24 hours. An inoculation loop was used totransfer a loop full of S. aureus from the plate to a 250 mL Erlenmeyerflask containing 100 mL of autoclaved tryptic soy broth. The flask wasthen placed in an incubator at 37° C. for 24 hours. After 24 hours, avolume of 1 mL of bacterial suspension was added to ten centrifuge tubeseach containing 1 mL of 50% glycerol as cryoprotectant. The mixture wasthen stored at -84° C. until further use.

S. aureus was cultured by adding a 2 ml aliquot of S. aureus that waspreviously frozen at −84° C. in 25% glycerol to a 250 mL Erlenmeyerflask containing 100 mL of sterile tryptic soy broth. The culture wasincubated in a shaker-incubator at 150 rpm and 37° C. for 24 hours. Thesuspension was washed three times with sterile deionized water and thefinal pellet was resuspended in 15 mL of deionized water. The number ofcolony forming units (cfu) in a suspension of S. aureus was determinedby serial dilution and viable plate counts. A series of 10-folddilutions (10-1 to 10-7) were prepared from the S. aureus suspension byadding 0.333 mL of sample to 3.0 mL sterile deionized water in adilution tube, followed by vortexing for 10 seconds. A volume of 0.1 mLof diluted sample was spread over the surface of tryptic soy agar usinga Teflon rod in each of three 100×15mm Petri dishes. The inoculatedplates were inverted and then incubated at 37° C. for 24 hours. Wherepossible, results were taken from plates that contained between 30 and300 colonies.

Organic dye or S. aureus suspension was applied to the test surfaces. Incase of organic dye, 0.02 mL of PR solution (2000 mg/L) or MO solution(2000 mg/L) was pipetted onto coated tiles and allowed to spread. Thedye-coated tiles were dried at 50° C. for 20 minutes in dark beforestarting the performance evaluation. In case of S. aureus, 0.1 mL of S.aureus suspension (2-3×105 CFU/mL) was pipetted onto each coated tilesurface and allowed to spread, giving a surface loading of 6400-9600CFU/cm². The tiles with S. aureus were dried in the dark in a biosafetycabinet for 3 hours.

The photocatalytic experiments were carried out under fluorescent lamps(General Electric model T8 Ultramax F28T8-SPX41) at visible lightirradiance of 1.8-2.0 W/m². The UVA irradiance (0.000 W/m²) was belowthe detection limit of the instrument consistent with no UV emissionfrom the fluorescent lamp spectra. The UVA irradiance (0.000 W/m²) wasbelow the detection limit of the instrument consistent with no UVemission from the fluorescent lamp spectra. The visible light and UVAirradiances were measured with a PMA 2140 Global detector or a PMA 2110UVA detector attached to a PMA2110 meter (Solar Light Co., Glenside,Pa.).

The temporal changes in dye concentration were determined by measuringthe absorbance after predetermined times of exposure to visible light.The inactivation of S. aureus was evaluated by determining the viablecounts after exposure to visible light.

Reflectance of coated or uncoated tile surfaces was measured with thePerkin-Elmer Lambda 800 with PELA-1000 Reflectance SpectroscopyAccessory (Perkin Elmer; Waltham, Mass.). Absorbance was calculated asthe negative log₁₀ of reflectance expressed as fraction. Coated tileswithout dye were used as the internal reference in the measurement. Dyedegradation was calculated according to:

${\% \mspace{14mu} {Dye}\mspace{14mu} {degradation}} = {\frac{A_{0} - A_{t}}{A_{0}} \times 100}$

where A₀ is the calculated absorbance of dye on coated tile beforeexposure to visible light and A_(t) is the absorbance of dye on coatedtile after exposure to visible light at a given time.

The inactivation of S. aureus was evaluated by determining the viablecounts after exposure to visible light. Bacteria were recovered byimmersing a tile in 20 mL PBS/SDS solution within a polypropylenecentrifuge tube and vortexing for 15 seconds. The tube was thensonicated at highest power for 1 minute. During sonication, the tube wasimmersed in a flowing water bath at 28° C. After sonication, the tubewas vortexed for 15 seconds. The viable bacteria in a volume of 0.1 mLsuspension from the centrifuge tube were enumerated as describedpreviously. The inactivation was calculated with the following equation:

${\% \mspace{14mu} {Inactivation}} = {\frac{{CFU_{0}} - {CFU_{t}}}{CFU_{0}} \times 100}$

where CFU₀ is the number of colonies at time zero and CFU_(t) is thenumber of colonies after time t.

The significance of visible light absorption by contaminant wasdelineated by employing filters to limit the wavelengths of visiblelight available for absorption. Four 400 nm longpass filters (2″×2″)were joined to form a square of 4″×4″ held together by transparent tape.The tiles coated with PR or MO dyes were prepared as stated above. Ineach set of experiment, four tiles were placed in a Petri dish. In caseof neutral filter experiments, the Petri dishes were covered with theirlids. In case of longpass filter experiments, the 4″×4″ filters wereplaced on the Petri dish without lids and the experiments were carriedout as above.

The Bioshield primer was applied directly from the manufacturer'scontainer. The A7+0.1PHF nanocomposites was prepared by adding 200 mg ofA7 to 180 mL of dilute NaOH solution (pH=9-9.5). The A7 suspension wassonicated (Misonix Sonicator 3000; Farmingdale, N.Y.) at the highestpower level providing 180-200 W for 30 minutes total (10 min on/2 minoff×3). A volume of 20 mL of PHF solution (1 mg/mL) was then added to A7suspension and mixed with magnetic stirrer for 10 minutes. Thisprocedure was repeated to accumulate a total volume of 5 L.

All surfaces (walls, ceilings, furniture, attached fixtures, etc.) weresteamed prior to coating to remove contaminants and ensure adhesion ofthe coating. After 15 minutes of drying, Bioshield primer was appliedusing an electric fogger (Model 2600, American Air & Water®, Inc.;Hilton Head Island, S.C.). After 15 minutes of drying time, theA7+0.1PHF formulation was applied to all surfaces.

Sterile cotton swabs were used to collect microbes from selectedsurfaces. A swab was immersed in sterile deionized water, followed bywiping on selected surfaces (2×2 in) back and forward 5 times. Microbesadhered to the wetted cotton were streaked on Tryptic soy agar plates.The plates were inverted and then placed in a 37° C. incubator. Colonyforming units (CFU) were counted after 48 hours of incubation.

It should be understood that the examples and embodiments describedherein are for illustrative purposes only and that various modificationsor changes in light thereof will be suggested to persons skilled in theart and are to be included within the spirit and purview of thisapplication.

1-19. (canceled)
 20. A visible light photocatalyst coating, comprising ametal oxide that in the presence of an organic contaminate absorbs atleast some visible light or comprising the metal oxide and an auxiliarylight absorbent that in the presence of an organic contaminate absorbsat least some visible light, wherein the metal oxide is a nanoparticleor microparticle or a film that contains crystallites of less than 50nm, whereby visible light catalyzes degradation of the organiccontaminate.
 21. The visible light photocatalyst coating according toclaim 20, wherein the metal oxide is a transition metal oxide, analkaline earth metal oxide, any combination thereof or a combinationthereof with an alkali metal oxide.
 22. The visible light photocatalystcoating according to claim 21, wherein the transition metal oxide is aoxide of titanium, vanadium, chromium, titanium, zinc, tin, cerium, orany combination thereof.
 23. The visible light photocatalyst coatingaccording to claim 22, wherein the oxide of 0titanium is TiO₂ in theform of anatase, rutile, or a combination thereof.
 24. The visible lightphotocatalyst coating according to claim 20, wherein the auxiliary lightabsorbent comprises a dye having an absorbance of light in at least aportion of the visible spectrum, polyhydroxy fullerene, fullerenes,carbon onions, graphene, or any combination thereof.
 25. The visiblelight photocatalyst coating according to claim 20, wherein the visiblelight photocatalyst coating is transparent.
 26. The visible lightphotocatalyst coating according to claim 20, wherein the crystallite isless than 10 nm.
 27. The visible light photocatalyst coating accordingto claim 20, wherein the organic contaminate is a microbe.
 28. Thevisible light photocatalyst coating according to claim 27, wherein themicrobe is a bacteria, a virus, a fungus, or any combination thereof.29. The visible light photocatalyst coating according to claim 28,wherein the bacteria is MRSA.
 30. The visible light photocatalystcoating according to claim 20, wherein the organic contaminate is anorganic pollutant.
 31. A suspension for applying the visible lightphotocatalyst coating according to claim 20, comprising: a metal oxide,wherein the metal oxide is a nanoparticle or microparticle that containscrystallites of less than 50 nm; and a liquid medium.
 32. The suspensionfor applying the visible light photocatalyst coating according to claim31, wherein the metal oxide is a transition metal oxide, an alkalineearth metal oxide, any combination thereof, or a combination of one ormore of the transition metal oxide and the alkaline earth metal oxidewith one or more alkali metal oxides.
 33. The suspension for applyingthe visible light photocatalyst coating according to claim 31, whereinthe transition metal oxide is a oxide of titanium, vanadium, chromium,titanium, zinc, tin, cerium, or any combination thereof.
 34. Thesuspension for applying the visible light photocatalyst coatingaccording to claim 33, wherein the oxide of titanium is TiO₂ in the formof anatase, rutile, or a combination thereof.
 35. The suspension forapplying the visible light photocatalyst coating according to claim 31,wherein the liquid medium is water, ethanol, toluene, or any combinationthereof.
 36. The suspension for applying the visible light photocatalystcoating according to claim 31, further comprising a suspending agent.37. The suspension for applying the visible light photocatalyst coatingaccording to claim 36, wherein the suspending agent is NaOH, Na₂CO₃, orNaHCO₃.
 38. The suspension for applying the visible light photocatalystcoating according to claim 36, wherein the suspending agent is asurfactant or polyethylene glycol.
 39. The suspension for applying thevisible light photocatalyst coating according to claim 31, furthercomprising an auxiliary light absorbent.
 40. The suspension for applyingthe visible light photocatalyst coating according to claim 39, whereinthe auxiliary light absorbent is a dye having an absorbance of light inat least a portion of the visible spectrum, polyhydroxy fullerene,fullerenes, carbon onions, graphene, or any combination thereof.
 41. Anantimicrobial device, comprising solid object coated with a visiblelight photocatalyst coating according to claim
 20. 42. The antimicrobialdevice according to claim 41, wherein the solid object comprises wood,metal plastic, glass, or a painted object.
 43. The antimicrobial deviceaccording to claim 41, wherein the solid object is a wall, rail,counter, light switch, bathroom fixture, or door knob.
 44. A method offorming an antimicrobial device according to claim 41, comprising:applying a suspension comprising a metal oxide, wherein the metal oxideis a nanoparticle or microparticle that contains crystallites of lessthan 50 nm, and a liquid medium to at least a portion of the surface ofa solid object; and evaporating the liquid medium.
 45. The method offorming an antimicrobial device according to claim 44, wherein the metaloxide is a transition metal oxide, an alkaline earth metal oxide, anycombination thereof, or a combination of one or more of the transitionmetal oxide and the alkaline earth metal oxide with one or more alkalimetal oxides.
 46. The method of forming an antimicrobial deviceaccording to claim 44, wherein the liquid medium is water, ethanol,toluene, or any combination thereof.
 47. The method of forming anantimicrobial device according to claim 44, wherein the suspensionfurther comprises a suspending agent.
 48. The method of forming anantimicrobial device according to claim 47, wherein the suspending agentis NaOH, Na₂CO₃, or NaHCO₃.
 49. The method of forming an antimicrobialdevice according to claim 47, wherein the suspending agent is asurfactant or polyethylene glycol.
 50. The method of forming anantimicrobial device according to claim 44, wherein the suspensionfurther comprises an auxiliary light absorbent.
 51. The method offorming an antimicrobial device according to claim 50, wherein theauxiliary light absorbent is a dye having an absorbance of light in atleast a portion of the visible spectrum, polyhydroxy fullerene,fullerenes, carbon onions, graphene, or any combination thereof.
 52. Themethod of forming an antimicrobial device according to claim 44, furthercomprising applying a primer to the solid object, whereby the surface ofthe solid object is a primed solid surface.